In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon structure is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist material, thickness uniformity of the photoresist material is a significant factor in achieving desired critical dimensions. The photoresist material should be applied such that a uniform thickness is maintained in order to ensure uniformity and quality of the photoresist material layer. The photoresist material layer thickness typically is in the range of 0.1 to 3.0 microns. Good resist thickness control is highly desired, and typically variances in thickness should be less than.+-.10-20 .ANG. across the wafer. Very slight variations in the photoresist material thickness may greatly affect the end result after the photoresist material is exposed by radiation and the exposed portions removed.
Application of the resist onto the wafer is typically accomplished by using a spin coater. The spin coater is essentially a vacuum chuck rotated by a motor. The wafer is vacuum held onto the spin chuck. Typically, a nozzle supplies a predetermined amount of resist to a center area of the wafer. The wafer is then accelerated to and rotated at a certain speed, and centrifugal forces exerted on the resist cause the resist to disperse over the whole surface of the wafer. The resist thickness obtained from a spin coating process is dependent on the viscosity of the resist material, spin speed, the temperature of the resist and temperature of the wafer.
After the resist is spin coated and selectively irradiated to define a predetermined pattern, the irradiated or nonirradiated portions are removed by applying a developer material. The developer material is also spin coated onto the wafer by applying developer material across the resist and then spin coating the developer material until centrifugal forces disperse the developer material over the coating of resist. Due to the surface of the photoresist material layer on the semiconductor being highly hydrophobic, the surface can repel the developer material at the initial state of jetting out the developer material from the developer supply nozzle so that turbulent flow of the developer material is generated on the surface of the resist forming bubbles. The bubbles produced between the photoresist material layer and the developer material are a cause of defects in the resist pattern. A solution to this problem has been to apply a washing solution material or liquid (e.g. water), that is typically used in a rinsing or washing process, onto the photoresist material layer and spin coat the washing solution material to form a washing solution material film. The developer material is then applied to the wafer and the spin coated onto the wafer and the washing solution material film is scattered off the surface of the photoresist material layer leaving only the developer material. After the photoresist material layer has been developed, the irradiated or nonirradiated portions are removed by rinsing or washing with the washing solution material. Each time the washing solution material is applied to the photoresist material layer, a washing solution nozzle is presented above the wafer and the washing solution material is applied. The washing solution nozzle then returns to its rest position and the developer nozzle moves to the center of the photoresist material layer and applies the developer material. The developer nozzle then moves to the rest position and the washing solution nozzle moves above the wafer to rinse the developed portions and the developer material off the photoresist material layer. This constant movement of the different nozzles not only takes up a great deal of time, but eventually leads to mechanical problems and increased maintenance.
A prior art developer nozzle and washing solution application system is illustrated in FIGS. 1a-1b. A multiple tip developer nozzle 10 is coupled to a pivotable arm 12 that pivots from a rest position to an operating position. In the operating position, the multiple tip nozzle 10 applies a developer material 26 on a resist layer 24 disposed on a wafer 22. The wafer 22 is vacuum held onto a rotating chuck 20 driven by a shaft 18 coupled to a motor 16. The developer material flows outward from the center of the photoresist material layer 24 covering the entire top surface of the photoresist material layer 24. A washing solution nozzle 28 is coupled to an arm 32 and moves from an operating position to a rest position. The washing solution nozzle supplies water by providing a washing solution material film prior to applying the developer material, and also providing a rinse to the developed portions and the developer material from the developed photoresist material 24. As illustrated in FIG. 1a, the washing solution nozzle 28 is typically at a much greater distance from the photoresist material layer in its operating state than the developer nozzle is when it is in its operating state resulting in a splashing effect that can result in scattering particles and causing defects. Furthermore, the developer nozzle 28 is specifically designed to apply a uniform layer of developer material, while the washing solution nozzle 28 is typically a water faucet type of arrangement and designed to rinse the developed photoresist off the wafer. Therefore, the washing solution nozzle does not have the advantages associated with the developer nozzle.
A common nozzle for applying both a developer material and a washing solution material has not been employed because the undesirability of the nozzle coming in contact with two completely different materials, which can affect the usefulness of each material. In view of the above, a nozzle is needed, for dispensing not only a uniformly thick layer of developer material across a photoresist material layer formed on a wafer, but also for dispensing a uniformly thick layer of washing solution material on the photoresist material layer, while substantially avoiding any mixing of the two materials with one another. Additionally, there is a need to eliminate the constant movement of the developer nozzle and the washing solution nozzle from the operating position to the rest position.